Electric heating unit



May 20, 1924. 1,494,937 C. C. ABBOTT ELECTRIC HEATING UNIT Original Filed Feb. 8 1922 Inventor: Charles C. JqbbO'bt His J 't'toPn e Patented mm,

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application l lel Iebraary 8, 198, Serial Io. 534,924. Renewed Ielu'aary 1!, me.

To all whom it may concern: Be it known that I, Cmnuzs C. Almo'rr, a citizen of the United States, residing at .Pittsfield, in the county of Berkshire,'State 5 of Massachusetts, have invented certain new and useful Improvements in Electric Heating Units, of which the following is a specification.

a My invention relates to electricheating units and has for its object improvements in sheath wire heating units. Y

. Morespecifically my invention relates to electric heating units of the sheath wire type in which a resistance element is em- 16 bedded in a coin acted mass of insulating material enclosed b for-"exam Is, as described and claimed in my Patent 0. 1,367,341, dated Februa 1,

1921. I have found that when ma ing 20 sheath wire heatingunits of relatively gr eat l en h, necemitatingthe use of Ion tubes, it is ifiicult' to keep the resistance e ement in a central position in the metallic sheath. This is due to'two causes; first, due to the difiiculty in holding a long resistance element centrally of the sheath while filling the sheath with powdered insulating material; and second, due to the fact that in the swafing operation the insulating material ten s to flow and pile u ahead 0 the swaging machine dies in suc manner as to force the resistance element from its central position into contact with the sheath, grounding the unit. 1' I 25 In accordance with my present invention I have provided insulating supports placed at intervals along the len h of the resistance conductor for positive y holding it centrally of the metallic sheath. I .havealso rovided a simple and reliable connection tween the terminal and the resistance conductor whereby the unit may be reduced in diameter to any desired extent without injury toeither the resistance conductor or the terminal.- In carrying out this part of my invention I have rovided'a recess in the terminal into whic the end of the sinuous resistance element isforced, the end of the terminal then being bent or pinched-on the resistance element to retain it in place.

For a more complete understanding of my invention refereuce'sliould be had to the accompanying drawing in which Fig; 1 is asectlon view showing an electric heating unit constructed in accordance with my iny a metallic sheath, such,

vention before the sw 'n' o ration; Fi

2 is an end elevation zi dw of l ig. 1; whil e Fig. 3 is a view partly in section showing the completed unit. 1

Referring to the drawin in one form of 00 my invention the elongated heating unit 10 comprises a sinuous or helical resistance ele- .ment 11 extending centrally of a metallic sheath 12. The resistance element is made of a suitable high resistance material having 05 considerable resiliency, such as nickel-chmmium alloy. Spacing or supporting insulators 13 are provided at intervals on the" resistance element for positively holding it centrally of the sheath. The supporting insulators consist of washers 14 of insulating material, such as"mica,'mounted on metallic eyelets 15. They are slip on the resistance element and spaced a ong its length as desired, the eyelets being then compressed or bent on the resistance element to hold the supporting insulators in place.

etallic terminals 16 and 17 are provided for the resistance element. Each terminal is formed with a longitudinal recess 18 into which the resistance elementis forced. for a short distance so as to enclose a plurality of turns, the end of the terminal then being bent or pinched over on the resistance ele-. ment to secure it in place. The recess 18 is slightly smaller than the resistance element which is contracted somewhat by twist- :ing, turning or screwing it with relation to the terminals when it is forced into the recess. When released, the resistanceelement uncoils inst' the inner surface of the recess, making a good electrical contact therewith, this contact being maintained by the resiliency of the resistance element.

In assembling the heating unit as shown 05 in Fig. 1, the resistance element with the spacing insulators and the terminals attached, as shown in the drawin is inserted in the metallic sheath 12. e sheath is closed at one end, for example, at the righthand end, by a solid washer 19 which fits on' terminal 17,'lfblding the terminal centrally j "of the sheath, the sheath being countersunk to receive the washer.- IA clip 20 is then slipped on terminal 17 and seated in a shallow groove in the terminal so as to hold the terminal against longitudinal movement under the tension of the resistance element. The resistance element is next stretched to a similar manner centrally of the sheath and against lon 'tudinal movement under the heat refractory insulatin material 23, such as magnesium oxide. 0 accomplish this the sheath is held. in an upright pos1t10n n a' special vibrating machine (not shown) with the end providedwith the star washer uppermost. As thesheath is filled with the insulating material through the openings in the star washer, it is vibrated to shake the insulating material together and distribute it uniformly around the terminals, the resistance element, and the supporting insulators 13. The supporting insulators fit loosely in the sheath so that the insulating material is free to pass around them, as well between the turns of the resistance element and through the centers of the supporting members. When the sheath has been filled, a solid washer 24 is inserted in lace around terminal 16 to close the tube. 0th ends of the sheath are'now pinched or bent at intervals 25, as shown in Fig. 2,so as to secure the washers in place.

The entire unit is now pased' through a swaging orrolling machine for the purpose of compacting theinsulating material within the sheath to a hard dense mass, the swag ing 0 eration reducin the diameter and increaslngthe length 0 the unit. It will be observed that during the swaging operation the insulating material will be prevented from piling up or flowing ahead of the swagmg machine die by the supporting insulators 13, and consequently the resistance element will be firmly embedded in the compacted insulatin material in a central position in the sheat The terminals 16 and 17 are gradualy reduced in diameter by the swag ng, the recessed ends contracting around the resistance element.

In case it is necessary to reducethe diameter of'the unit considerabl in order to obtain the desired length or fbr any other reason, it may be desirable to pass the unit through the swaging machine a number of times so as to re uce its diameter gradually. In this event the unit may be annealed between the successive swaging operations. By means of my invention I have been enabled to construct heating units of any desired length and to reduce their diameter by swaging, for example, from g" before swaging to 1;" after swaging, the unit being an-.

nealed several times during the course of this reduct on. After the unit has been swaged to the desired extent, the washers F at each end and the clips are cut off or.

otherwise removed and the ends of the unit provisions of the patent statutes, it should 4 e understood that I do not limit my invention thereto, since various modifications thereof will suggest themselves to those which is set" forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. An electric heating unit comprising an elongated sheath, a resistance element extending lengthwise in said sheath, insulatin supports for said resistance element space along the length thereof, and powdered in ing supports for said resistance element seskilled in the art without departing from 5 the spirt of my invention, the scope of cured at intervals along the length thereof,

and powdered heat refractory insulating material within said sheath compacted to a hard dense mass around said resistance .7

element.

3. An electric heating unit comprising an elongated sheath, a helical resistance element extending lengthwise in said sheath,

insulating supports for said resistance element secured'atintervals along the length thereof, terminals recessed to fit tightly over the ends of said resistance element, and powdered heat refractory insulatin material within said sheath compac to a hard dense mass around said terminals and said resistance element.

4. The method of for m ning an electric heating unit which consists in mountin a resistance element fcentrally of a meta 'c sheath on insulating supports s aced at in-.

tervals along the-length thereo filling the sheath with powdered insulating material and then compacting the insulating material around the resistance element.

e 5. The method of forming an electric heating unit which-consists in securing insulating supports along the length of a sinuous reslstance element, inserting the same in a metallic sheath, filling the sheath with powdered heat refractory insulating material, and then compacting the insulating material to a hard dense. mass around the, resistance conductor by reducing the sheath.

P6. The method of forming an electric f heating unit which consists in securin insulating supports along the length of a elical resistance element, securing terminals to the resistance element, inserting the same in a metallic sheath, filling the sheath with powdered heat refractory insulating material, and then com acting said insulating material to a hard ense mass around the terminals and resistanceelement by reducing the sheath,

An electric heating unit comprising an elongated sheath, 'a sinuous resistance element extending lengthwise of said sheath, a terminal for said resistance element provided with a recess into which the resistance element is forced so as to be maintained in rovided with a longitudinal recess adapted to receive a plurality of turns 0 the conductor and having its end bent over to secure the conductor in place, and powdered heat refractory insulating material within said sheath com acted to a hard dense mass around sai resistance element and said terminal.

9. An electric heating unit comprising an elongated sheath, a helical resistance element extending lengthwise in said sheath,

terminals for said resistance element each provided with a recess into which a plurality of turns of said resistance element are forced so that said resistance element is sulating material within said sheath compacted to a'hard dense mass around said resistance element and said terminals.

'10. The method of forming an electric heating unit which consists in connecting terminals to a helical resistance element by forcin the resistance element into recesses in sai terminals by twist' the resistance element to contract it, bending the ends of said terminals over to secure the resistance element in place, inserting the whole in-a metallic sheath, filling the sheath with powdered insulating material, and then compacting the insulatin material around the resistance element an the terminals.

In witness whereof, I have hereunto set my hand this second da of Februa 1922.

CHARL S C. ABB TT. 

